Re: [Xen-devel] loading IDT in xen?

To:	"余上" <yusunn@xxxxxxxxx>
Subject:	Re: [Xen-devel] loading IDT in xen?
From:	"Jun Koi" <junkoi2004@xxxxxxxxx>
Date:	Thu, 31 Jan 2008 16:29:42 +0900
Cc:	xen-devel@xxxxxxxxxxxxxxxxxxx
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On 1/31/08, 余上 <yusunn@xxxxxxxxx> wrote:
> There is another IDTR reload in x86_32.S at line 15 , where the
> protected mode IDT vectors are initialized with ignore_int handler
> firstly. Then trap_init called from __xen_start will setup the formal
> IDT vectors .

Now I see that. But the the question is: why we have to setup a
"dummy" IDT in trampoline.S like that???

Thanks,
Jun


>
> 2008/1/31, Jun Koi <junkoi2004@xxxxxxxxx>:
> > I am looking at the hypervisor code to see how Xen setup the IDT. But
> > it seems that the code in protected mode reuses the real mode IDT?
> >
> > In arch/x86/boot/trampoline.S we have at several places:
> >
> > lidt bootsym(idt_48)
> >
> > And idt_48 is defined as:
> >
> > idt_48: .word 0,0,0 # base = limit = 0
> >
> > And in nowhere we initialize idt_48, which means idt_48 reuses real
> > mode IDT table. However, real mode IDT table has different format than
> > protected mode IDT, so this doesnt look to work for me.
> >
> > Definitely I miss something here. Anybody could enlighten me how IDT
> > setting in protected mode work?
> >
> > Thanks,
> > Jun
> >

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